388 .' MESSRS. V. H. VELET AND J. J. MANLEY ON 



The acid may therefore be regarded as anhydrous (HN0 3 ) within the limits of 

 experimental error. Hitherto the highest recorded values appear to be 99'45 per 

 cent. (PERKIN),* 99'67 per cent. (LuNGE and REv),t and 99'84 per cent. (ROLE),} 

 but doubts have been expressed as to the correctness of the determinations of the 

 last observer. 



CALIBRATION OF CELL AND WIRES USED FOR ANHYDROUS ACID. 



As the method originally proposed by KOHLRAUSCH and adopted by subsequent 

 workers for determining the " resistance capacity " of their cells appeared in this 

 particular case to involve manipulative difficulties and errors consequent therefrom, 

 the following method was used. The distance between the inner surface of the 

 electrodes was determined along nine different lengths ; the mean value found 

 was 9'77 centims. ; the volume of the portion of the cell between the electrodes was 

 measured by water delivered from a calibrated burette connected with the cell by 

 pressure-tubing, readings being taken for the levels of the upper surface of the 

 lower electrode and lower surface of the upper electrode. Five or six series of 

 experiments were conducted, different burette levels being taken in each such series; 

 the mean of all the values was 35 '2 cub. centims., with an error of '1 P er cent. 

 From these data the mean cross sectional area was calculated to be 3'603 sq. centims. 

 In order to determine the resistance of the platinum leads sealed into the cell, 

 their lengths were measured and the resistance of a known length of the same wire 

 determined by CAREY FOSTER'S method , the value thus calculated was added to 

 that of the copper wire leads which joined the cells to the bridge, due allowance 

 being made in each case for its coefficient at the temperature of the experiment. 

 Such indirect measurements cannot, of course, lay claim to absolute accuracy, but. 

 appeared to be the best attainable after the cell had been fitted up and used for the 

 experimental determinations. 



(i.) Chemical Properties of Anhydrous Acid. 



As a considerable quantity of the anhydrous acid was prepared in the course of 

 the enquiry some of its properties were examined. It has no action upon the 

 following rnetals (i.) copper, (ii.) silver, (iii.) cadmium, (iv.) mercury, all of a high 

 degree of purity, and (v.) commercial magnesium at ordinary temperatures ; purified 

 iron and commercial granulated tin were unaffected by the acid even when boiling. 

 Zinc purified by frequent distillation in vacuo was slightly acted upon at ordinary 

 temperatures, but sodium immediately caught fire. The acid has no action whatever 



* ' Journal of the Chemical Society,' 1893 (Trans.), p. 65. 



t ' Journal of the Society of Chemical Industry,' 1891, p. 543. 



J 'Ann. Chim. Phys.' [4], vol. 10, p. 140. 



